This invention is based on and claims the benefit of priority from the Japanese Patent Applications No. 11-141491, filed May 21, 1999; No. 11-305560, filed Oct. 27, 1999; and No. 2000-006731, filed Jan. 14, 2000, the entire contents of which are incorporated herein by reference.
This invention relates to an optical information processing apparatus, and more particularly to a compact, general-purpose optical information processing apparatus capable of various types of filtering and image processing.
When various types of information, including images and signals, are recognized or classified, the degree of similarity of those to the comparison reference are generally calculated and then they are recognized or classified.
A combination of a matched filter (MSF) and a correlating unit or a joint transform correlating unit (JTC) has been used as means for calculating the degree of similarity.
While those methods have a sufficient performance in recognizing and classifying known, simple pieces of information cut off from the background, they have to process even pieces of information contributing less to recognition and classification, when directly processing images or signals with complex features. This is one factor which causes errors.
In addition, they respond sensitively even to a slight transformation, rotation, enlargement, or reduction, which often produces errors.
As for filters that allow transformation, noise, or the like, tremendous research effort has been directed toward filters using coordinate transformation, such as Fourier Mellin (FM) transformation, Synthetic Discriminate Function (SDF) filters, Circular Harmonic Expansion (CHE) filters, and other filters of these types.
As for the processing of complex objects, many investigations have been recently made of the technique for, instead of directly processing various types of information, such as images or signals, transforming them into features contributing much to recognition or classification, object by object in pre-processing, and recognizing them on a neural network or the like, using the transformed features.
In the pre-processing, correlation values obtained from the aforementioned MSF or JTC, edge images obtained through convolution by a Laplacian filter, feature extracted images obtained by wavelet transformation or Gabor transformation, Fourier spectrum images, or the like have been used.
In general, when two-dimensional images are processed, serial calculations on an ordinary computer are not practical, because it takes an extremely long time. It is therefor clear that an optical method capable of two-dimensional batch processing is superior in time.
Although having such superiority, the optical image processing method has hardly been put to practical use.
One reason is that there is no general-purpose optical information processing apparatus which enables the user or developer to execute various types of processing (optical information processing).
Although each of the various types of filters researched and developed until now has been excellent, they represent only one part of component technology in the field of practical industrial applications. They are not so convenient as electronic image processing boards commercially available at present and have often not been used in seeking the solution to the actual problems.
FIG. 37 shows the optical information processing apparatus disclosed in Jpn. Pat. Appln. KOKAI Publication No. 8-129149 form a different point of view.
With the optical information processing apparatus, the image to be processed is displayed on a first liquid-crystal display 2. Then, the image is read via a collimator lens 4 by the laser light emitted from a semiconductor laser 3. A first lens 5 performs Fourier transform optically.
Then, the image subjected to Fourier transform is produced on a second liquid-crystal display 6. Then, a filtering function form a memory 7 is displayed on the second liquid-crystal display 6, thereby filtering the image. After the filtered image is subjected to inverse Fourier transform using a second lens 8, a photodetector 9 can process the image.
The problem of the image processing apparatus the present invention tries to solve will be explained by reference to FIG. 24 schematically showing the optical information processing apparatus of FIG. 37.
The image displayed on an image display section 1101 is read by the read light generated by a read light generator section 1102.
A Fourier transform optical system 1103 obtains the Fourier transform of light that read the image and forms its Fourier transform image in the back focal plane of the Fourier transform optical system 1103.
The filtering of the Fourier transform image is done by displaying a filtering function on a filtering section 1104 located in the vicinity of the back focal plane of the Fourier transform optical system 1103.
An inverse Fourier transform optical system 1105 subjects the filtered light to inverse Fourier transform. The result is obtained by a filtering image acquiring section 1106.
In such an image processing apparatus, the spatial optical modulator, or the image display section 1101, has been only as large as a filtering liquid-crystal display with a small number of pixels and a small display area.
In recent years, however, as the liquid-crystal apparatuses and DMD (digital micromirror apparatuses) have included more and more pixels, this provides a wider selection of spatial optical modulators, which has satisfied the need for an increasing capacity of images to be processed.
At the same time, the entire computing apparatus has been required to be more compact.
To make the computing apparatus more compact, it is necessary to shorten the focal length f of the Fourier transform optical system 1103.
As shown in FIG. 24, however, when the size Wi of the input image is made larger and the focal length f of the Fourier transform optical system is made shorter, the angle 2xcex8i of the light entering the filtering section 1104 becomes greater.
For simplicity sake, FIG. 24 shows only the DC component which has no frequency component in the frequency components included in the image displayed on the image display section 1101.
On the other hand, the light entering the filtering section 1104 further produces diffracted light through the pixel structure of the spatial optical modulator constituting the filtering section 1104.
The light passed through the filtering section 1104 spreads at a specific angle in the direction opposite to the direction of incidence. The diffracted rays each spread in a similar manner.
Consequently, the light of diffraction of 0th order (light of 0th order) from the object observed overlaps with the light of the +first-order or xe2x88x92first-order diffraction (the +first-order light or xe2x88x92first-order light), which makes it impossible to acquire the properly filtered image.
The another problem of the image processing apparatus the present invention tries to solve will be explained by reference to FIG. 25 schematically showing the optical information processing apparatus of FIG. 37.
To simplify explanation, FIG. 37 shows a cross section of the image processing apparatus taken along the optical axis and only the rays of light corresponding to the DC component whose spatial frequency component is zero in the spatial frequency components included in the image displayed on an image display section 2001.
In the image processing apparatus of FIG. 37, the image displayed on the image display section 2001 is read by the read light generated at a read light generator section 2002.
Then, the light reading the image is inputted to a Fourier transform optical system 2003, which forms the Fourier transform image of the input image on its back focal plane.
A filtering section 2004 is placed in the vicinity of the back focal plane on which the Fourier transform image is formed and filters the Fourier transform image.
The filtered light is subjected to inverse Fourier transform at an inverse Fourier transform optical system 2005. The result is obtained by a filtering image acquiring section 2006.
With such an image processing apparatus, the light concentrates in an area in the vicinity of the optical axis which corresponds to no spatial frequency component in the Fourier transform image formed at the filtering section 2004, whereas the light decreases in an area faster than the optical axis which corresponds to higher spatial frequency components.
Thus, to effect filtering accurately, a high-contrast spatial optical modulator is needed as the filtering section 2004.
In the spatial optical modulator used as the filtering section, for example, a twisted nematic liquid crystal of a frequently used type achieves only a contrast ratio of about 20:1, and a ferroelectric liquid crystal of the same type achieves only a contrast ratio of about 200:1.
Since an ordinary image often has the important information in areas other than the area where the spatial frequency component is zero, applying the contrast ratio of the spatial optical modulator, such as liquid crystal, directly to the image processing apparatus prevents the spatial frequency components near zero from being cut off sufficiently, which can cause light leaks. This might make the desired filtering impossible.
For example, consider a case where high-pass filtering is effected to prevent light in the region of almost no spatial frequency as shown in FIG. 26B, when one-dimensional distribution of the amount of light is as shown in FIG. 26A.
In this case, it would be ideal if the result of filtering would be as shown in FIG. 2D. If the contrast ratio at the filtering section that effects filtering were insufficient, light could not be cut off sufficiently, because of the amount of light is too large in the region of almost no spatial frequency. Thus, the result of filtering would be as shown in FIG. 26C, which might be different from what has been expected.
Furthermore, in an image processing apparatus as shown in FIG. 25, the spatial optical modulator, or the image display section 2001, has been only as large as a filtering liquid-crystal display with a small number of pixels and a small display area.
In recent years, however, as the liquid-crystal apparatuses have included more and more pixels, this provides a wider selection of spatial optical modulators, which has satisfied the need for an increasing capacity of images to be processed. At the same time, the entire computing apparatus has been required to be more compact.
To make the entire computing apparatus more compact, it is necessary to shorten the focal length f of the Fourier transform optical system 2003.
As shown in FIG. 25, however, when the size Wi of the input image is made larger and the focal length f of the Fourier transform optical system 2003 is made shorter, the angle 2xcex8i of the light entering the filtering section 2004 becomes greater.
As described above, in the optical system with the large angle 2xcex8i of the bundle of incident rays, the components in the vicinity of the region where the spatial frequency component is zero are larger than those in the remaining areas. This requires the filtering section 2004 to have a higher contrast ratio. Therefore, use of the present special optical modulator makes it more difficult to achieve high-accuracy filtering.
It is, accordingly, an object of the present invention to provide a compact, general-purpose optical information processing apparatus capable of various types of filtering and image processing.
Another object of the present invention is to overcome the aforementioned drawbacks and provide an optical image processing apparatus capable of obtaining correctly filtered images, making a compromise between a trend toward a larger input image and a trend toward a smaller apparatus.
Still another object of the present invention is to provide an optical image information processing apparatus capable of assuring more accurate filtering by correcting the contrast ratio which is insufficient in a spatial optical modulator with a relatively low contrast ratio usually used in filtering.
According to a first aspect of the present invention, there is provided an optical information processing apparatus comprising: an image display section for displaying information on an object to be processed as image information; an image information reading section for converting a light from a light source into collimate light and projecting the collimate light onto the image display section to read image information; a Fourier transform optical system for obtaining the Fourier transform of the image information read by the image information reading section; an image dividing section for dividing the image information subjected to Fourier transform at the Fourier transform optical system; a filtering section for filtering the phase or amplitude information in one piece of the image information divided by the image dividing section; an inverse Fourier transform optical system for obtaining the inverse Fourier transform of the image information filtered at the filtering section; a filtering image information acquiring section for taking in the image information subjected to inverse Fourier transform at the inverse Fourier transform optical system; and a Fourier transform information acquiring section for taking in the other piece of the image information divided by the image dividing section.
According to a second aspect of the present invention, there is provided an optical information processing apparatus comprising: an image display section for displaying information on an object to be processed as image information; an image information reading section for converting a light from a light source into collimate light and projecting the collimate light onto the image display section to read image information; a first Fourier transform optical system for obtaining the Fourier transform of the image information read by the image information reading section; an image dividing section for dividing the image information subjected to Fourier transform at the first Fourier transform optical system; a first filtering section for filtering the phase or amplitude information in one piece of the image information divided by the image dividing section; a first inverse Fourier transform section for obtaining the inverse Fourier transform of the image information filtered at the first filtering section; a second Fourier transform optical system for obtaining the Fourier transform of the image information subjected to inverse Fourier transform at the first inverse Fourier transform section; a second filtering section for filtering the phase or amplitude information in the image information subjected to Fourier transform at the second Fourier transform optical system; a second inverse Fourier transform section for obtaining the inverse Fourier transform of the image information filtered at the second filtering section; a filtering image information acquiring section for taking in the image information subjected to inverse Fourier transform at the second inverse Fourier transform section; and a Fourier transform information acquiring section for taking in the other piece of the image information divided by the image dividing section.
According to a third aspect of the present invention, there is provided an optical information processing apparatus comprising: an image display section for displaying information on an object to be processed as image information; an image information reading section for converting a light from a light source into collimate light and projecting the collimate light onto the image display section to read image information; a first Fourier transform optical system for obtaining the Fourier transform of the image information read by the image information reading section; a first filtering section for filtering the phase or amplitude information in the image information subjected to Fourier transform at the first Fourier transform optical system; a first inverse Fourier transform section for obtaining the inverse Fourier transform of the image information filtered at the first filtering section; a second Fourier transform optical system for obtaining the Fourier transform of the image information subjected to inverse Fourier transform at the first inverse Fourier transform section; a second filtering section for filtering the phase or amplitude information in the image information subjected to Fourier transform at the second Fourier transform optical system; a second inverse Fourier transform section for obtaining the inverse Fourier transform of the image information filtered at the second filtering section; and a filtering image information acquiring section for taking in the image information subjected to inverse Fourier transform at the second inverse Fourier transform section.
According to a fourth aspect of the present invention, there is provided an optical image processing apparatus comprising: an image display section for displaying an image to be processed; a read light generator section for generating light to read an image displayed on the image display section; a Fourier transform optical system for obtaining the Fourier transform of the image read from the image display section by the light from the read light generator section; a filtering section with a pixel structure for filtering the image subjected to Fourier transform at the Fourier transform optical system; an inverse Fourier transform optical system for obtaining the inverse Fourier transform of the light filtered by the filtering section; and a filtering image acquiring section for acquiring the image subjected to inverse Fourier transform at the inverse Fourier transform optical system, wherein the display size Wi of the image display section, the wavelength xcex of the read light, the focal length f of the Fourier transform optical system, the minimum pixel-to-pixel spacing p of the filtering section, the display size Wf, and the incident angle xcex8g to the filtering section are so selected that the diffracted light of 0th order generated at the filtering section never overlaps with another n-th order diffracted light.
Specifically, the filtering section has two axes crossing at right angles along which a large number of pixels are arranged in a matrix and, when Wi greater than Wf holds along each of the axes, satisfies the following expression:
arctan(Wi/2f) less than arcsin(xcex/2p cos xcex8g)xe2x80x83xe2x80x83(1)
Furthermore, specifically, the filtering section has a display element for displaying a function corresponding to filtering to be done and a diffraction grating adjacent to the display element, with the pitch p of the diffraction grating satisfying
nxc3x97q=pxe2x80x83xe2x80x83(2)
where n is a natural number, and the diffraction grating aligning with the pixel structure and satisfying the following expression in place of expression (1):
arctan(Wi/2f) greater than arcsin(xcex/2q cos xcex8g)xe2x80x83xe2x80x83(3)
According to a fifth aspect of the present invention, there is provided an optical image processing apparatus comprising: an image display section for displaying an image to be processed; a read light generator section for generating light to read an image displayed on the image display section; a Fourier transform optical system for obtaining the Fourier transform of the image read by the read light generator section; a filtering section for filtering the image subjected to Fourier transform at the Fourier transform optical system; an inverse Fourier transform optical system for obtaining the inverse Fourier transform of the image filtered by the filtering section; a contrast ratio correcting section for correcting the contrast ratio of the filtering section; and a filtering image acquiring section for acquiring the image filtered at the filtering section.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.